In general, a shock absorber damps vibration of a vehicle, a device, a structure, and the like. JP 2006-183864A discloses a shock absorber for damping vibration associated with the steering of a two-wheel vehicle. This shock absorber includes a tubular cylinder, a fluid chamber, a piston, piston rods, a flow channel, a tank, and a pressure control valve. The fluid chamber is formed inside the cylinder and filled with a working fluid. The piston partitions the fluid chamber into two compartments. The piston rods are provided on both sides of the piston. The two compartments communicate with each other via the flow channel. The tank is connected to an intermediate point of the flow channel and has the working fluid reserved therein. The pressure control valve is provided at an intermediate point of the flow channel. With this shock absorber, no matter which direction the piston moves in, control is performed so that the pressure in a contracted compartment acts as a valve opening pressure for the pressure control valve. As such, this shock absorber can produce a damping force caused by the resistance of the pressure control valve.